The pre-eruptive behavior of the Campi Flegrei caldera before the eruption of 1538 has been reconstructed for the first time. The study, signed by INGV, University of Rome Three, Federico II, USGS, Rome La Sapienza, Second University of Naples, was recently published in Scientific Reports of Nature
Geological, archaeological, historical results, laboratory analyzes and mathematical models have made it possible to reconstruct for the first time the precursory phenomena of the only eruption that took place in the Campi Flegrei caldera in historical times and the dynamics of the rising magma that fed it. The multidisciplinary work, carried out by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), the Universities of Roma Tre, Federico II, Roma La Sapienza, the United States Geological Survey (USGS) and the Second University of Naples, reconstructed the essential elements of the pre-eruptive magma transfer in the 1538 eruption. The study Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption (link: www.nature.com/articles/srep32245), was published on Scientific Reports di Nature
"Predicting eruptions, particularly in highly dangerous volcanoes, is the challenge that volcanology must face today," says Mauro Di Vito, Senior Researcher at the Vesuvius Observatory of INGV (OV-INGV). “Some volcanoes show a predictable and constant behavior, combined with a low hazard, others show greater variability, with a consequent increase in hazard if characterized by large magmatic systems and located in densely populated areas. This is the case of the Campi Flegrei caldera, on the western outskirts of Naples, commonly considered as the most dangerous volcano in the world".
Although the last eruption took place in 1538, the Campi Flegrei have been subject to numerous episodes of crisis in recent decades, linked to ground movements, surface seismicity and degassing. Despite the various studies carried out on the Campi Flegrei, until now the methods of surface propagation of the magma were not yet known, not even before the eruption of 1538. This is a crucial problem, which could provide valuable information for predicting the movement of the magma and the possible opening of eruptive vents, in any future reactivation of the system.
"The research made it possible to reconstruct for the first time the precursory phenomena of the only eruption that took place in the Campi Flegrei caldera in historical times and the dynamics of the magma ascent that fueled this eruption", adds Di Vito. Traditional techniques of geology, geomorphology, paleontology and geochronology have been integrated by analyzes of historical and archaeological sources and mathematical models to accurately define the dynamics of subsidence and uplift of the ground (bradyseism) in the caldera over the last 2000 years, with particular attention to the period during which the eruption of Monte Nuovo took place (1538). “The ground movements have been defined and reconstructed in twenty points located along the entire Phlegraean coast, from Capo Miseno to Nisida (Fig. 1). And the interpretation of the results has allowed the reconstruction of the transfer of pre-eruptive magma to Campi Flegrei both in the short term (pre-1538) and in the long term (last 5000 years) (Fig. 2 and 3), with definition of the relative areas of parking. In particular, despite the repeated upheavals in the central part of the Flegrea caldera, the eruptions systematically took place at the edge of the uplifted area”. This study makes it possible to better define and interpret the phenomena underway in the caldera and helps to predict the location of future eruptive vents, with clear repercussions on the mitigation of volcanic risk. “This model”, concludes Mauro Di Vito, “is also in agreement with the monitoring data of other active calderas that have recently erupted in the world, which show similar behaviours, with eruptions at the margins of the raised area before the eruption. This suggests that such behaviors constitute an important key to the general understanding of caldera dynamics.
Abstract
Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggests a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera center, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that was feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.
Fig. 1. Map of the Campi Flegrei caldera on a digital terrain model. The following are reported: the eruptive centers active between 15.000 and 9.500 years ago (circles with broad hatching), the eruptive centers active between 8.600 and 8.200 years ago (circles with dense hatching) and those active between 4.800 and 3.800 years ago (green circles). The red lines represent the main faults and the black line the edge of the caldera formed 15.000 years ago, during the eruption of the Neapolitan Yellow Tuff. The yellow ellipse and the cross represent the most uplifted area in the last 5.000 years and the center of the caldera, respectively. The green ellipse represents the surface projection of a pressurized ellipsoidal body, the source of the recent deformations of the caldera and located about 4 km deep. The black squares are the points for which the ground movements in the last 2000 years have been defined and in particular in connection with the deformation phases that led to the eruption of Monte Nuovo. The blue line represents the cliff of the marine terrace of La Starza, an area submerged and then raised in the last 10.000 years by about 100 m in connection with the main eruptive phases of the caldera. The insert shows the frequency of eruptive vents in the last 5.000 years as a function of the distance from the center of the caldera. Of note, the maximum concentration of vents occurs between 3 and 5 km from the center of the caldera and at the edges of the area of maximum uplift.
Fig. 2. Localization of the sources of ground deformation in the long period (1400–1536) and in the short period immediately preceding the 1538 eruption (1536–1538). The white line on the map indicates the trace of the sectional view showing the depth and position of the magma sources in the two periods mentioned (b). In black on the sources the error bars. Below (c) the soil deformation profiles along the coast, in the two periods mentioned.
Fig. 3. Model of magma transfer before the Monte Nuovo eruption (orange). The magma first moves laterally from an oblate-shaped magma source (OMR) located about 4.6 km deep below the center of the caldera and feeds an eccentric magma chamber, under Monte Nuovo (Monte Nuovo Reservoir, MNR) about 3.8 km deep. depth. From this the magma propagates vertically forming a smaller and more superficial magma chamber and then feeds the eruption. The other vertical arrows indicate the same mechanism of magma ascent, responsible for some eruptions that have occurred in the caldera over the last 5.000 years. Our reconstruction suggests the following general conceptual model for magma transfer in calderas (right images): a tabular magma intrusion (sill) forms above a central magma chamber, fed by a dike (red line) and resulting from stacking other tabular intrusions (purple lines). The sill determines the uplift of the central part of the caldera where the emplacement of the previous sills has produced the resurgence of the caldera. The shear stresses are concentrated at the edges of the sill (orange line) which propagates laterally following the minor component of the stress. At the edges the sill changes its slope and becomes a subvertical dyke and feeds eruptions at the edges of the more uplifted area (black triangles).